Pump



July 31, 1962 J. A. LAUCK ETAL PUMP Filed March 23, 1959 FIG. 6

3 Sheets-Sheet 3 M X W us g. FIG. 7 6 I24 I20 1 22K xx x FIG. 8 g

54 A xxx; 2 54 I4 1 $3.; k zz/ 4 ATTORNEY 3,346,932 on n This invention relates to a pressure loaded pump, and more particularly to a pressure loadable sealing or thrust plate for such a pump.

As is well known, in a pressure loaded gear pump of the type including one set of axially movable or floating pressure loadable sealing or thrust plates, the discharge pressure or a part thereof, is applied to the rear or motive surface of each floating thrust plate to urge said plates into sealing engagement with the associated gears.

In general, the use of such thrust plates have enabled significant improvements to be made in the gear pump art in terms of increased volumetric efliciency and significantly higher discharge pressures. However, one serious problem which has been encountered in the use of such thrust plates has involved the clearance provided between the rear face of the plate and the associated face of the pump housing which forms the chamber into which the pressurized fluid is conducted for applying motive force against the rear face of the plate. In all known former pumps of the type contemplated this clearance has been made as small as possible within the requirement that a chamber be provided in which pressure fluid can function to properly urge the thrust plate into sealing engagement with the gear side face. As a result, serious difiiculties have been encountered from time to time in the use of such pumps. A known construction in accordance with the prior art in this respect is disclosed in the co-pending application Serial No. 801,052, filed March 23, 1959, now Patent No. 3,003,426, in the name of John A. Lauck.

It will be realized that the aforementioned clearance should be as small as is feasible, but, on the other hand, cannot be so small that an inadequate pressure chamber volume results. It has been found in practice that in relatively small gear pumps, for example, a chamber clearance of .005" or greater may be required, whereas in relatively large gear pumps the required chamber clearance may be .025. Under these circumstances, the failure of one or more seal rings, which are normally associated with gear pump thrust plates in order to seal off the pressure chambers from communication with a low pressure mea in the pump, tends to render the pump totally inoperative; i.e., the over-all efficiency of the pump tends to decrease to zero, since a complete loss of pressure tends to be encountered in the pressure chamber upon such seal ring failure. The loss of chamber pressure occurs through the pump bearings, which are associated with the rotating shafts mounting the gears, and permits fluid at discharge pressure to enter between the thrust plate and the gear side face, and the thrust plate to be thereupon forced away from the gear side face a distance which is equal to the clearance in the pressure chamber. The resulting relatively large clearance between the previously abutting sealing surfaces of the gear and thrust plate normally results in a substantially complete failure of the pump to generate discharge pressure of any significant value.

In addition, the use of a small chamber clearance of, for example, .005" as aforesaid, in an efiort to reduce the loss of pump pressure in the event of a seal ring failure, creates another problem. That is to say, a small fixed chamber clearance tends to cause a non-uniform pressure in the chamber because of the resulting slow flow of leakage fluid from the discharge side of the pump into the p essure chamber. Pump discharge pressure may, of

course, vary rapidly across a wide range of pressures with variations in demand on the pump. In the use of prior constructions using a relatively small fixed clearance of, say, .005, the chamber pressure tends to vary substantially at difierent locations within the chamber during a change in demand on the pump and prior to stability of discharge pressure at a relatively fixed value. This causes an unbalance of the thrust plates which, as is well-known is undesirable. Also, the response of the thrust plates to a change in discharge pressure tends to be sluggish.

We have found that by changing the form of the rear or motive surface of the thrust plate, or of the adjacent housface, to provide a substantially increased pressure chamber volume, while at the same time providing a substantially decreased end clearance between the thrust plate and the adjacent surface of the pump body, that the foregoing problems are largely overcome. For example,

in g

in one embodiment of this invention there is provided an inwardly tapered or converging motive surface whereby the pressure chamber is substantially enlarged in volume while a substantially decreased end clearance, the value of which depends in part upon the pump capacity and pump operating conditions, is provided. The result is that in the event of a seal ring failure and consequent loss of discharge pressure in the thrust plate chamber with consequent movement of the thrust plate away from the gear face a distance equal to the end clearance, pumping efficiency does not decrease to substantially zero, as heretofore, but the pump will continue to operate at a reduced efficiency. It will be appreciated that a given end clearance for a given capacity pump will function as set out above only within a limited range of operating conditions. Substantial changes in pressure and/or temperature of the fluid being pumped, as well as the use of a fluid of substantially different viscosity, may influence to a marked degree the optimum end clearance for best results. Preferably, the end clearance dimension should be application engineered depending, upon the pump capacity to be used and the effected operating conditions to be encountered. It may be pointed out at this time that in gear pumps utilizing our invention, it will seldom be necessary to use an end clearance greater than .005". This compares with a much larger clearance pressure chamber and end clearance dimension in many pumps manufactured in accordance with the previous state of the art. This is of extreme significance when it is considered that such pumps are frequently used as vital components in complex and expensive hydraulic systems and machines, the operation of which is dependent upon continued operation of the pump.

For instance, such pumps are generally used as supply pumps in jet aircraft fuel systems. If the scaling rings of one or more Such pumps should fail as aforesaid, the pump will, according to the present invention,

continue to be capable of delivering to the engine a sufficient quantity of fuel to sustain flight under all conditions of flight. However, with previous constructions such was not the case since a substantially total loss of pumpin ,efficiency would ensue.

In addition, the taper of the motive surface of the thrust plate, according to the above mentioned embodiment, may be such as to provide a chamber size which insures continuously equal pressure throughout the chamher.

The foregoing exemplary embodiment of our invention is only illustrative, since the principle thereof may be embodied in many different forms, as will appear hereinafter.

It is an important object of the present invention to provide an operationally improved gear pump.

It is another important object of the invention to provide improved thrust plate means for gear pumps.

Patented .luly 31, 1952 pump essentially inoperative.

A' still further object of'the invention'is to provide a pressure loaded. gear pump "wherein a thrust chamber configuration is provided which effects generally improved operation of the pump such that the pump continues to function at reduced eificiency in the event of loss of fluid pressure in the thrust chamber while providing a'substantial thrust chamber volume.

Another object of the invention is to provide a gear pump having a thrust plate with an end clearance of .005 or lessland a thrust pressure'ch'amber of substantially larger depth so that loss of sealing pressure on the thrust plate does not result in a substantially complete loss of pump efiiciencyand the pressure chamber volume is always adequate'to provide rapid thrust plate response topressure fluid communicated to. the chamber. i The above and further objects, features, and advantages of this invention will appear to those familiar with the artin the following detailed description and with reference to the accompanying drawings, wherein:

FIGURE 1 is an axial cross-sectional view illustrating an intermeshing gear type pump incorporating one embodiment of the present invention;

FIGURE 2 is a cross-sectional view of the pump taken along line 2-2 of FIGURE 1; FIGURE 3 is an enlarged broken-away sectional view of a portion of the pump as shown in' FIGURE 1; FIGURE 4 is a view in perspective of the thrust plate of FIGURE 3;. and

FIGURES 5, 6, 7 and 8 are enlarged broken-away sectional views of 'a portion of the pump shown in FIGURE 1, but each incorporating a modified thrust plate and/or chamber construction.

1 Referring now in detail to the drawings, the numeral 10 denotes a suitably chambered gear pump housing in which are rotatably mounted driven gear 12 and an in- I rermeshin driving gear 14. Driven gear 12 is supported on a'shaft 16 journalled on its right side in a roller bearing. 18 and ou'its left side in a roller bearing 20,'

Roller bearing 18 is located in a chamber 22 formed in the pump housing and is maintained in position by a fixed thrust plate 24 located intermediate bearing 18'and gear 12 and providing an annular recess 26 in registry with the left end portion of the bearing. The bearing memberis located in a housing chamber 28 and is located in registry with an annular recess portion 30 of an axially movable thrust plate 32 intermediate said bearing and the one side face of gear12.

Driving gear 14 is mounted for rotation upon a drive shaft 34 journalled on its right side in a roller bearing 36 and intermediate its ends in a roller bearing 38, said roller bearings being mounted in chambers 40 and 42, respectively, in a manner similar to the mounting of bearings '18 and 20. A fixed thrust plate 44 is mounted intermediate gear 14' and bearing 36 in a manner similar to the mounting of thrust plate 24, said plates 24 and 44 mating in sealing relationship along complementary flat surfaces thereof indicated at numeral 46. An axially movable interrupted annular thrust plate 48 is mounted intermediate gear 14 and bearing 38 in a manner similar tothe mounting of movable thrust plate 32, said' movable thrust plates abuting 'in sealing relationship along complementary flat surfaces or'interruptions (FIGURES J 2' and 4) thereof as indicated at numeral 50. The construction of thrust plates '32 and 48 will be described in detail hereinafterg A cover body 54. having an adaptor connecting flange 56 and a surface 58 is secured to the pump body 19 by means of a plurality of bolts, one of which is shown at numeral 60. I

seal retainer 66 in chamber 64. A plurality of O-rings are mounted in annular grooves formed in various of the parts of the pump construction to provide sealing means. The O-ring 70 provides a seal between retainer member 66 and cover body 54; O-ring 72 provides a seal between the pump body 10 and cover body 54. Sealing O-rings 74 adn176 are located in recesses 78 and 80 of thrust plates 32 and 48, respectively ancl provide a seal' between each thrust plate and the respective bearing members 2t and 42.

As shown in FIGURE 2, the pump body It has an inlet conduit 34 formed in its left side and an outlet conduit 86 formed in its right side. Pressure generated by the gears is communicated from the outlet or discharge side of the pump to the rear or motive surfaces 88 and 90 of the thrust plates 32 and 48, respectively, through passage ways 92 and 94 in said thrust plates. The discharge pressure fluid is'directed through passage 92 into a'chamber' 96 which is formed between the inner surface of cover body 54 and the motive surface of thrust plate 32, and' through passage 94' into a chamber 98 which is formed between the said cover body surface and the motive sur- As discharge pressure is applied relationship to the abutting side surfaces of gear 14, and,

likewise, the corresponding inner facing surfaces of thrust I plates 24 and 32 are maintained in sealing relationship with the adjacent faces of gear 12. In order to provide an initial seal between the inner facing surfaces of the thrust plates and the gears, a plurality of compression springs, one of which is illustrated at numeral 100, are disposed in recesses 192 formed in the peripheral portion of each of the thrust plates 32 and 48. v 5

Referring now particularly to FIGURES 3 and 4, wherein a portion of the pump, including thrust plate 48, is shown in enlarged view, it will be noted that the motive surface 90 of the thrust plate is tapered inwardly from A shaft seal'62 is located in an enlarged chamber 64 l u of cover body 54 between a seal retainer member 66 and an interrupted annular flat end portion 106. As pointed out hereinabove, the preferred end clearance between the flat surface 106 and the adjacent face of cover body 54 may vary from, say, .001" to .003", or even .005 and larger, depending upon the pump capacity, other pump design characteristics, and pump operating conditions to be encountered in operation such as pressure and temperature and viscosity of the fluid to be pumped. It is generally desirable to maintain this clearance as small as feasible for'the particular pump application and size of pump involved. Of course, byminirnizing the end clear ance the loss of efliciency of the pump in the event of a failure of the sealing ring will be minimized. The tapered motive surface of thrust plate 48 should provide adaquate volume in chamber 98 so that variations in discharge pressure will be immediately transmitted through passage 94 to sections of the chamber remote" from the passageway. We have found in practice that a 5 taper provides a good designin this respect, although, u

of course, the degree of taper may be varied, within limits, as desired, depending, in part, uponthe size of the pump.

Referring to hearing 42, for example, it will be understood that pressure fluid in chamber 98 cannot leak past the mating, surfaces of the bearing cage and the pump housing bore inasmuch asfthe bearing is shrunk fit in the bore. The same is true of the remaining roller bearings.

Sealing O-ring'76 prohibits leakage from the chamber through theinn'er roller section of the bearing in which shaft 34' is mounted. However, in the event of a seal ring' failure pressure-fluid'from chamber 98 can escape to the inlet'of the pump by way' of theinner roller portion of the bearing, the shaft seal chamber 108, and passage means, not shown, connecting the shaft seal chain her to the pump inlet. Likewise, pressure fluid will escape 1 from chamber 96 through bearing 30 and chamber 28 to the pump inlet in the event of 'a'failure of seal ring 74.

In such an event, discharge pressure fluid in the pump 'A ain, the shoulder 11? rovides will force apart the sealing surfaces of the thrust plate and gear side face resulting in a movement of the thrust plate leftwardly until the flc'; portion 105 abuts the inner surface of cover body 54. it is apparent that by minimizing the end clearance the dimension of the path of leakage fluid passing from the discharge to the inlet side of the pump between the sealing faces of the thrust plate and gear is minimized.

In the modification of the invention shown in FIGURE 5, like parts are numbered the same as in FIGURE 3. In FlGUI- E 5 the thrust plate 11% is modified in form to provide an annular pressure chamber 111 radially inwardly of an annular shoulder 112, which provides minimum end clearance with the opposing face of the cover body 54.

in FIGURE 6 another modified thrust plate design 114 is shown in association with which an annular pressure chamber lid is formed radially outwardly of a shoulder 118 which is located adjacent the sealing ring recess. minimum end clearance.

In the modification illustrated in FEGURE 7 a planar motive surface 1.2% of a thrust plate 122 is provided in conventional manner. An interrupted annular shim 124 is mounted between the outer peripheral portion of plate 322 and the cover plate surface 58. It functions in the same manner as shoulder ill/Z of FIG RE 5. Gf course, the shim could be of smaller diameter and located radially inwardly of its FEGURE 7 position, as is shoulder 118 in FEGURE 6.

In the modification of FlGURE 8 an enlarged pressure chamber is provided between the planar motive surface of the thrust plate 126 and the facing surface of an annular recess formed in the cover body 54-. Minimum end clearance is provided between the peripheral portion of the thrust plate and the overlapping portion 13% of the cover body 54.

It will be understood that numerous other modifications can readily be conceived which utilize our invention, the above described embodiments being merely illustrative. For example, the annular shoulder portions 112 and 113 provided in FlGURE-S 5 and 6 might just as readily comprise a few projecting teeth spaced annularly one from the other about one or more selected diameters of the thrust plate. Also, thePlGURE 8 embodiment is subject to many variations. In addition it will be recognized that body portion It? can readily provide a radially inwardly extending annulus between body 54 and the floating thrust plates in accordance with the invention. The objectives of the invention would also be satisfied, for example, if shim 324 of FEGURE 7 were replaced by an annular proiection for instance, integral with pump body 14 and extending radially inwardly of body it? and intermediate the thrust plate and the cover body 54 so as to provide end clearance between the right side of the proiection and the adjacent motive surface.

From the foregoing it will now be understood that the present invention effects a significant advance in the art of pumps utilizing thrust plates by providing an enlarged chamber adjacent the motive surface of each plate Within which pumping pressure functions to urge the thrust plate into sealing relationship with the abutting side face of the gear. Then, by utilizing any feasible thrust plate 'or pump housing design which provides minimum end clearance between the thrust plate and the housing, the pump remains capable of functioning to deliver reasonably high pressure with reduced efiiciency in the event of loss of pressure in the pressure chamber. in addition, our in-v vention provides a thrust plate pressure chamber of sufii- V cient volume to insure full pumping pressure throughout the pressure chamber at all times.

l rom the foregoing, it is believed that those familiar with the art will readily recognize, appreciate and understand the novel concepts and features of the improved pumping mechanism herein described and shown. Obviously, while the invention has been related to a particular few embodiments, numerous changes and substitutions of equivalents may be made Without necessarily departing from the scope and intent of the invention concerned. As a result, it is not our intention to be limited to any particular form of the invention herein llustrated and described except as may appear in the following appended claims.

We claim:

1. In a pressure generating pump of the type including a housing containing intermeshing gears and having an leading to and an outlet leading from said housing, an socially movable sealing member having a sealing surface engageable with a side face of one of the gears and a motive surface remote from the sealing surface, a pump housing surface in facing relation to said motive surface,

means separating said motive surface from said housing surface to form a pressure chamber therebetween, said pressure chamber communicating with a pump generated pressure for urging the sealing surface of the sealing member into sealing engagement with the side face of the gear, said separating means providing an effective end clearance between the chamber forming surfaces, said end clearance restricting the axial movement of the sealing surface of the sealing member in a direction away from the adjacent side face of the gear to a distance equivalent to the said end clearance such that the pump generates a substantial fluid pressure at a reduced efficiency in the event of loss of said sealing engagement following a loss of pump generated pressure in one of said pressure chambers.

2. A fluid pump as claimed in claim 1 wherein said end clearance does not exceed .005.

3. A fluid pump as claimed in claim 1 wherein said end clearance is at least .061" but does not exceed .065.

4. A fluid pump as claimed in claim 1 wherein said end clearance is at least .061 but does not exceed .003".

5. A fluid pump comprising a housing having a pump chamber formed therein, said housing having an inlet leading to and an outlet leading from said pump chamber, means including a rotatable member received in said pump chamber eifective to force fluid from said inlet out of said housing through said outlet, means defining an axially adjustable thrust plate received in said pump chamher and having a sealing surface engageable with the adiacent side face of said rotatable member to provide a pumping seal therewith, and a motive surface on the thrust plate facing away from the rotatable member, a cover member housing fixed opposing surface located in facing relationship to said motive surface, and interfering means intermediate said motive surface and said opposing surface maintaining said surfaces in axially spaced relation whereby to form a pressure chambertherebetween, said pressure chamber communicating with a pump generated pressure for urging said sealing surface into sealing engagement with the adjacent side face of said rotatable member, and said interfering means being located in predetermined close axially spaced relation to the adjacent surface to restrict axial movement of the thrust plate in a direction away from its sealing engagement with the side face of said rotatable member such that the pump contin use to function at reduced efficiency after loss of sealing engagement between the adjacent side face of said rotatable member and said sealing surface while a relatively large pressure chamber volume is provided between the motive and opposing surfaces.

6. A fluid pump comprising a housing having a pump chamber formed therein, said housing having an inlet leading to and an outlet leading from said pump chamber, means including a rotatable pump member received in said pump chamber for pressurizing fluid from the inlet to the outlet, an axially movable thrust plate received in said pump chamber and movable into sealing engagement with the side face of said pump member to provide apumping seal therewith, a motive surface on said thrust plate facing av ay from said pump membena cover memtinues to function to deliver reduced 'ber having an opposing surface in facing relation to said motive surface, means intermediate said motive surface and opposing surface, the space between said latter surfaces forming a pressure chamber which communicates with a pump generated pressure which is applicable to 'said motive surface for maintaining sealing engagement a housing containing intermeshing gears and having an inlet leading to and an outlet leading from said housing, an axially -movable thrustplate associatable in sealing :relationship with a side face of one of said gears, the

side of said thrust plate remote from said side face comprising a motive surface subject to a pump generated pressure and located in'facing relation to the housing, a

shaft member extending axially of said one gear and thrust plate and supporting same in the housing, said motive surface having an inner and an outer periphery relative to the axis of the shaft, said outer periphery and V the housing forming an end clearance therebetween which does not exceed .005", and an interrupted annular tapered surface connecting said peripheries forming one side of a pressure chamber of varying dimension between said peripheries such that the pump generates a substantial fluid pressure at a reduced efliciency in the event of loss of sealing relationship following a loss of pump generated pressure in one of said pressure chambers.

8. In a pressure-generating pump of the type including a housing containing intermeshing gears and having an inlet-leading to and an outlet leading from said housing,

' an axially movable thrust plate associatable in sealing relationship with a side face of one of said gears, the side of said thrust plate remote from said side face comprising a motive surface subject to a pump generated pressure, a

'shaft member extending axially of said one gear and thrust plate and supporting same in the housing, a cover member having an opposing surface facing said motive surface for forming a pressure chamber therebetween, and an interrupted annular shoulder projecting outwardly from said motive surface for spacing said motive surface from said'opposing surface and for providinga motive surface end clearance between said interrupted annular shoulder and said 'opposing'surface not exceeding .003" such that the pump continues to function at reduced efliciency after loss of sealing relationship between the adjacent side face of said gear and said sealing surface while a relatively large pressure chamber volume is provided between the motive and opposing surfaces.

' 9. In a pressure-generating pump of the type including 'a housing containing intermeshing gears and having an inlet leading to and an outlet leading from said housing, an axially movable thrust plate associatable in sealing relationship'with a side face of one of said gears, theside of said thrust plate remote from said side face comprising amotive surface subject;- to a pump generated pressure, a shaft member extending axially of said one gear and thrust plate and supporting same in the housing, acover 7' -member' having an opposing surface facing" said motive surface, and projecting means extending from the motive surface towards the opposing surface such that said projection meansforms with said opposing surface an end r clearance dimension not exceeding .005","thereby causing a chamber of substantial vvolume intermediate'the motive surface and the opposing surface to be formed while providing a relatively small end clearance between the motive surface and the opposing surface so that the pump generates a substantial fluid pressure at a reduced efficiency in the event of loss of said sealing relationship following a rlossrof pump generated pressure said chamber. V

10. In a pressure-generating pump of the type including a housing containing inter-meshing gears and having an inlet leading to and an outlet leading from said hou sing, an axially movable thrust plate associatable in sealing relationship with a side face of one of said gears, the side of said thrust plate remote from said side face comprising a motive surface subject to a' pump generated pressure, a shaft member extending axially of said one gear and thrust plate and supporting same in the hous ing, a cover member having an opposing surface fac ing said motive surface, and a shim means located between the motive surface and the opposing surface for maintaining same in spaced relation whereby to provide a pressure chamber, said shim means forming with said opposing surface an end clearance not exceeding i003" such that the pump will continue to operate at a reduced efiiciency in the event of loss of sealing engagement between the adjacent side face of said gear and said thrust plate following a loss of pump generated pressure in one of the pressure chambers. a

11. :In a pressure-generating pump of the' type including a housing containing intermeshing gears and'having 1 an inlet leading to and an outlet leading from said housing, an axially movable thrust plate associatable in sealing relationship with a side face of one of said gears, the side of said thrust plate remote from said side face comprising a motive surface subject to a pump generated pressure, a shaft member extending axially of said one gear and thrust plate and supporting the same in the housing, a cover member having an opposing surface facing said motive surface, means projecting from said opposing surface toward said motive surface such that said projecting a means forms with said motive surface an end clearance dimension not exceeding .005, whereby the pump gencrates a substantial fluid pressure at a reduced efficiency in the event of loss of sealing engagement between said gear side face and said thrust plate pump generated pressure.

12. In a pressure-generating pump 'of thetype includ- 7.

ing a housing containing intermeshing gears and having an inlet leading to and an outlet leading from said housing, an axially movable thrust plate associatable in sealing relationship with a side face of one of said gears, the

side of said thrust plate remote from said side face come prising a motive surface subject to a pump generated pressure, a shaft member extending axially of said one gear and thrust plate and supporting same in the housing; a 'cover member having an opposing surface facing said motive surface in recessed relation thereto whereby to form a pressure chamber therewith, a shoulder extending forwardly of said recessed opposing surface toward said motive surface to provide an end clearance between said shoulder and the motive surface which is at 'least .001" but does not exceed .003" such that therpump will operate at a reduced efliciency in the event of loss of 1 said sealing relationship following a loss of V pump ,generated pressure in said pressure chamber. a

i 113. As an article of manufacture, a thrust plate for use with gear pumpscomprising an interrupted annular, member having an annular seal ringtrecess formed intone" L side thereof, an interrupted annular fiat portion formed You said side in the outer peripheral portion of the side,

; and a radially inwardly tapered surface on said side conouter, periphery of saidrecess. 7

c 14. As an article of manufacture, a thrust plate for use r with gear pumps comprising an interrupted annular'memher having an annular seal ring recess formed in one side 5 thereof and intermediate inner and outer peripheries of meeting the inner periphery of said flat portion with the following a loss of the member, and an annular projection extending axially outwardly from said side and located on said side radially intermediate said recess and the outer periphery of the thrust plate.

15. As an article of manufacture, a thrust plate =for use with gear pumps comprising an interrupted annular memher, said member having an inner periphery defining an annular opening, an annular bearing recess formed in one side of the thrust plate radially outwardly of said opening, an annular seal ring recess formed in said one side of the thrust plate radially and axially outwardly of said bearing recess, and an interrupted annular projection extending axially outwardly of said one side and radially outwardly of said seal ring recess.

16. As an article of manufacture, a thrust plate for use with gear pumps comprising an interrupted annular memher, said member having an inner periphery defining an annular opening in said member, an annular bearing recess formed in one side of the thrust plate radially out- Wardly of said opening, an annular seal ring recess formed in said one side of the thrust plate radially and axially outwardly of said bearing recess, and projecting means extending axially outwardly of said one side and radially outwardly of said sealing ring recess.

References Cited in the file of this patent UNITED STATES PATENTS Appel Aug. 17, Beust June 23, Seyventsen Oct. 25, Compton Dec. 7, Kane Aug. 9, Harrington et al. Oct. 11, Eames May 21, Lauck May 28, Miller et al. Oct. 15, Murray Dec. 17, Hilton July 8, Aspelin Sept. 30, Booth et a1 Apr. 12, Specht et al. May 31,

FOREIGN PATENTS Great Britain Oct. 15, Italy Apr. 19, Great Britain Oct. 19, Great Britain Nov. 27, France Mar. 17, France Jan. 12,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,046,902 July 31, 1962 John A. Lauck et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

, Column 4, line 7, for "adn" read and column 6,

line 48, for "housing" read having a; column 7 line 13 for "to said end clearance with the side face" read with the side face to said end clearance ---5 line 69 for "projecting" read projection column 9, line 25 for sealing? read sea Signed and sealed this 20th day of November 1962.,

(SEAL) Attest:

DAVID L. LADD ERNEST W. SWIDER Commissioner of Patents Attesting Officer 

